An infusion pump infuses fluids, medication or nutrients into the circulatory system of the patient being treated. Infusion pumps are used to administer fluids in ways that would be impractically expensive or unreliable if performed manually by nursing staff. Commercial infusion pumps can administer injections as small as tens of nanoliters in a single injection and typically can deliver less than 100 microliters per hour on a continuous basis. These delivery volumes levels are too small for a drip and the delivery rate and timing are not practical for manual injections. Infusion pumps can deliver injections on a scheduled time interval, for example every minute, and can deliver injections with repeated boluses requested by the patient, up to pre-selected maximum number per hour (e.g. in patient-controlled analgesia). Infusion pumps can also be programmed to deliver fluids whose volumes vary by the time of day.
Because they can also produce quite high pressures, infusion pumps can also inject controlled amounts of fluids subcutaneously (beneath the skin), or epidurally (just within the surface of the central nervous system—a very popular local spinal anesthesia for childbirth). Different types of infusion include—but are not limited to:                Continuous infusion usually consists of small pulses of infusion, usually between 20 nanoliters and 100 microliters, depending on the pump's design, with the rate of these pulses depending on the programmed infusion speed.        Intermittent infusion has a “high” infusion rate, alternating with a low programmable infusion rate to keep the cannula open. The timings are programmable. This mode is often used to administer antibiotics, or other drugs that can irritate a blood vessel.        Patient-controlled Analgesia is infusion on-demand, usually with a preprogrammed ceiling to avoid intoxication. The rate is controlled by a pressure pad or button that can be activated by the patient. It is the method of choice for patient-controlled analgesia (PCA).        Parenteral Nutrition usually requires an infusion curve similar to normal mealtimes.        Patient-controlled Epidural Analgesia (PCEA) is a related term describing the patient controlled administration of analgesic medicine in the epidural space, by way of intermittent boluses or infusion pumps. This is most commonly used by terminally ill cancer patients.        
Although the use of infusion pumps for very small volumes of often very potent drugs has begun, the accuracy of infusion pumps is still an issue. A recent study of commercially available infusion pumps has found significant errors in delivery volumes. In some cases the amount delivered over a long periods, as is typically used in calibration, may be accurate to a few percentage. But the delivered volume over short time scales and delivery rates have been found to vary by as much as 50% from the target settings. Over-dosing or under-dosing can result in adverse short term responses to potent drugs and multiple requests for dosing. Significant variations in delivery volume with temperature have also been found. This has resulted in limiting the use of infusion pumps to therapies where the detrimental effects of overdosing and under-dosing are limited. Highly potent medications delivered in small volumes are not candidates for today's infusion pump technology.
The reasons for errors in delivery are several. Many infusion pumps use disposable syringes as the pumping chamber. These use single-use or disposable syringes and therefore, are ideal to avoid potential cross contamination of medication. However these type syringes vary and the force required to move the syringe piston, or plunger, a given distance to deliver a given volume may not be the same from one syringe to the next. This variation in force without a suitable feedback control system will result in errors in delivered volume. Additionally the delivery volume variations from current technology pumps have been found with changing temperatures. A main factor for this variation may also be changing viscosity of the medications with temperature. Delivery volumes are also affected by the back pressure or resistance to the injection. To take advantage of the infusion pumps' ability to deliver medications under pressure that enables subcutaneous injections and epidural injections requires careful control of the delivery volumes even with varying backpressure or resistance to injection offered in the biological environment. Other factors that are not yet understood may also be significant. There is a need for a system to ensure accurate and reproducible delivery volumes and delivery pressure (would this not be primarily delivery volumes—the pressure may vary depending on the actual parts so that delivery volumes are accurate; of course we could use force control as well to ensure accurate delivery pressures).
Additionally new mechanisms are being developed, or have been developed, to drive (administer) the injection (and/or infusion). Simplified mechanisms are being found that can deliver the dosages required using both gravity and spring driven pump mechanisms. These simple systems eliminate motor drives and the associated electronics and their high power consumption. These systems can offer new levels of reliability and compactness, with considerably reduced cost?. There is a need however for new control mechanisms.
Closed loop feedback control mechanism are known in robotics, mechanics and machine control. However these control methods are still missing from medical devices such as infusion pumps. Traditional servo motor drives include proportional integral and derivative position loop (PID) and proportional position loop integral and proportional velocity loop (PIV) feedback control schemes, as well as other non-linear control schemes. Hereinafter the aforementioned schemes will be referred to simply as “feedback control schemes” (does this sound ok—if not please feel free to use some other term). There is a need to develop such feedback control schemes for use with motor driven infusion pumps. Additionally the simple non-motor driven infusion mechanisms require control means that are equivalently effective. The known feedback control schemes, PID and PIV, do not necessarily apply directly to a non-motor driven pump system. New control schemes are required that delivery very small volumes accurately and reproducibly regardless of the method use to drive the pump. New schemes are required for a motor driven syringe, a spring driven syringe, a gravity feed, a spring bag, a peristaltic pump and others. The control schemes must be able to adapt to the unique sources of variation in the medical and biological application of infusion pumps. The control schemes must provide accurate delivery volumes over time with changing temperature, viscosity, back pressure and manufacturing variations in mechanism components.
The apparatuses proposed here can be used either directly, or with simple modifications, for all the different infusion methods used in the medical field. Note that the apparatuses presented here do not represent an exhaustive list, and are simply representative of the approach presented here. Apparatuses that can be derived by extension, by those skilled in the art, are therefore included in the intended scope of this application.